The present invention relates generally to the field of devices which provide the ability to speak for people whose larynxes have been removed or rendered inoperative. Specifically, the invention relates to the category of such devices in which pressurized air from an external source is used to actuate a vibratory member, thereby producing a tone which is transmitted to the proximity of the pharyngeal cavity for articulation.
A patient undergoing mechanical ventilation cannot speak due to the interruption of air flow to the larynx as a result of the patient being intubated or tracheotomized. In addition, a patient may be rendered unable to speak after having undergone a laryngectomy to remove a diseased or damaged larynx. In either case, the inability to speak can be most frustrating. This problem can result in severe emotional distress in the case of quadriplegic patients, who cannot write or gesture, and are thus left with no means whatsoever to communicate effectively.
Various types of artificial speech devices have been developed to address this problem. One type, which has shown promise recently, comprises a tone-generating mechanism (usually a vibratory reed), which is actuated by an external source of pressurized air. The reed, which is housed externally to the patient, produces a tone which is then transmitted, via a nasal catheter, to the pharyngeal region of the patient, so that speech sounds can be articulated by the mouth. The flow of air to the tone-generating mechanism is started and interrupted by a solenoid valve, which can be actuated by a hand switch, or by a switch operated by the wrinkling of the patient's brow, as disclosed in U.S. Pat. No. 4,338,488, for example.
While devices of this type have demonstrated satisfactory results, their operation is at times sensitive to conditions of obstructed air flow downstream from the tone generator. Obstructed, or partially obstructed, air flow can occur when mucous or saliva enters the patient end of the nasal catheter, or when the catheter becomes twisted or kinked. The result is an increase in air flow resistance, which translates as a buildup of pressure on the upstream side of the tone-generating reed. This increase in upstream pressure will, above a certain level, collapse the reed, making the device inoperative. If air from the pressurized source continues to flow without pressure relief, damage can occur to the device.
Therefore, some means has been sought to allow the tone-generating mechanism to operate even with a restricted air flow, and to provide overpressure relief in the event of a total or near total air flow blockage in the catheter.